1. Field of the Invention
The present invention relates to a fluid control apparatus that performs fluid control and a method for adjusting the fluid control apparatus.
2. Description of the Related Art
PCT Publication No. 2008/069264 discloses an existing fluid pump.
FIG. 10 is a diagram showing a pumping action of the fluid pump in PCT Publication No. 2008/069264 in a third-order resonant mode. The fluid pump shown in FIG. 10 includes a pump body 10, a diaphragm 20 fixed at its outer peripheral portion to the pump body 10, a piezoelectric device 23 attached to a center portion of the diaphragm 20, a first opening 11 formed in a portion of the pump body 10 that faces substantially the center portion of the diaphragm 20, and a second opening 12 formed in an intermediate region between the center portion and the outer peripheral portion of the diaphragm 20 or in a portion of the pump body that faces the intermediate region. The diaphragm 20 is made of metal, and the piezoelectric device 23 covers the first opening 11 and does not reach the second opening 12.
In the fluid pump shown in FIG. 10, when a voltage having a predetermined frequency is applied to the piezoelectric device 23, the portion of the diaphragm 20 that faces the first opening 11 and the portion of the diaphragm 20 that faces the second opening 12 flexurally deform in opposite directions. Thus, a fluid is sucked through one of the first opening 11 and the second opening 12 and discharged through the other.
With regard to the fluid pump having a structure as shown in FIG. 10, the structure is simple and it is possible to make the fluid pump thin. Thus, for example, the fluid pump is used as an air-transport pump for a fuel cell system. However, an electronic apparatus into which the fluid pump is incorporated constantly tends to be decreased in size, and thus the fluid pump is required to be further decreased in size without diminishing the capability (flow rate and pressure) of the fluid pump. As the size of the fluid pump is decreased, the capability (flow rate and pressure) of the pump is diminished. Thus, when it is attempted to decrease the size of the pump with its capability maintained, there is a limit on the fluid pump having an existing structure.
Therefore, the inventor of the present application has conceived a fluid pump having a structure described below.
FIG. 11 is a cross-sectional view showing the configuration of a principal portion of the fluid pump. The fluid pump 901 includes a cover plate 95, a base plate 39, a flexible plate 35, a spacer 37, a diaphragm 31, and a piezoelectric device 32, and has a structure in which these components are laminated in order. In the fluid pump 901, the piezoelectric device 32 and the diaphragm 31 joined to the piezoelectric device 32 constitute an actuator 30.
An end portion of the diaphragm 31 is adhesively fixed via the spacer 37 to an end portion of the flexible plate 35 having an air hole 35A formed at its center. Thus, the diaphragm 31 is supported by the spacer 37 so as to be spaced apart from the flexible plate 35 by the thickness of the spacer 37.
In addition, the base plate 39 having an opening 40 formed at its center is joined to the flexible plate 35. A portion of the flexible plate 35 that covers the opening 40 is able to vibrate with substantially the same frequency as that of the actuator 30 by variation in the pressure of a fluid associated with vibration of the actuator 30.
That is, due to the configuration of the flexible plate 35 and the base plate 39, the portion of the flexible plate 35 that covers the opening 40 becomes a movable portion 41 that is able to flexurally vibrate, and an outer side portion of the flexible plate 35 with respect to the movable portion 41 becomes a fixed portion 42 that is restrained by the base plate 39. It should be noted that the movable portion 41 includes the center of a region of the flexible plate 35 that faces the actuator 30.
In addition, the cover plate 95 is joined to a lower portion of the base plate 39, and an air hole 97 is provided in the cover plate 95 and communicates with the opening 40.
In the above structure, when a drive voltage is applied to the piezoelectric device 32, the diaphragm 31 flexurally vibrates due to expansion and contraction of the piezoelectric device 32, and the movable portion 41 of the flexible plate 35 vibrates with the vibration of the diaphragm 31, in the fluid pump 901. Thus, the fluid pump 901 sucks or discharges air through the air hole 97.
Accordingly, in the fluid pump 901, since the movable portion 41 of the flexible plate 35 vibrates with the vibration of the actuator 30, it is possible to substantially increase the vibration amplitude. Thus, the fluid pump 901 is able to obtain a high discharge pressure (hereinafter, referred to as “pump pressure”) and a high flow rate even though the fluid pump 901 is small in size and low in height.
Here, the natural vibration frequency of the flexible plate 35 is determined by the diameter of the movable portion 41, the thickness of the movable portion 41, the material of the movable portion 41, the tensile stress of the movable portion 41, and the like. As the natural vibration frequency of the flexible plate 35 is closer to the drive frequency of the drive voltage applied to the fluid pump 901, the movable portion 41 of the flexible plate 35 vibrates more with the vibration of the actuator 30.
However, the shape of each component constituting the fluid pump 901 is varied for each fluid pump 901, and there is a limit on the accuracy of positioning when each component is laminated. Thus, the natural vibration frequency of the flexible plate 35 is varied for each fluid pump 901.
Therefore, it is difficult to closely adjust the natural vibration frequency of the flexible plate 35 in the fluid pump 901 to an optimum value at which a desired pump pressure equal to or higher than a predetermined value is obtained with power consumption within an allowable range.